Conventionally Practiced Art
The CZ method (Czochralski method) is a method in which melt is kept in a crucible within a CZ furnace; a dopant is supplied to the melt; a pulling mechanism pulls up, from the melt, a silicon single crystal having the dopant added thereto; and the silicon single crystal grows.
To impart an electrical property of N type to the silicon single crystal, a dopant (impurity element) for the N type, such as arsenic As, phosphorus P, and antimony Sb, is added to the silicon single crystal. Of those dopants, arsenic As and phosphorus P are sublimable dopants, and change directly from the solid phase to the gaseous phase at a relatively low temperature. There has been conventionally carried out a dopant supplying method in which the dopant is added to the silicon crystal by: lowering an accommodation chamber accommodating the sublimable dopants from the upper part in the CZ furnace to a prescribed position above the melt; heating the dopants accommodated in the accommodation chamber by radiant heat radiated from the melt to evaporate; and, introducing, from the accommodation chamber to the melt, the dopant that has becomes the gas as a result of the evaporation. Conventionally, as a method for introducing the dopant as described above, there has been provided a blowing method in which the dopant is introduced to the melt using a carrier gas, by positioning an opening end of a supplying tube to a prescribed position higher than the melt; and blowing the carrier gas from the supplying tube to the melt by using an inert gas such as argon gas as the carrier gas for transporting. As another method, there has been proposed a submerging method in which the supplying tube is submerged into the melt to introduce, from the supplying tube to the melt, the dopant that has become the gas as a result of evaporation.
(Conventional Art as Described in the Patent Document 1)
In the Patent Document 1, a tube assembly for supplying an impurity element is attached to a seed chuck of the pulling mechanism; the tube assembly for supplying the impurity element is lowered by the pulling mechanism until a dopant accommodation chamber of the tube assembly for supplying the impurity element is positioned about 285 mm above the melt surface; and, arsenic in the accommodation chamber is heated at this position by radiant heat radiated from the melt to evaporate. And, the tube assembly for supplying the impurity element is further lowered by the pulling mechanism until the supplying tube of the tube assembly for supplying the impurity element is contacted with the melt; and, the arsenic vapor is introduced from the supplying tube to the melt. Here, the position at which the dopant evaporates (position of about 285 mm above the melt surface) is obtained in advance from a result of analysis of a thermal model.
(Conventional Art as Described in the Patent Document 2)
In the Patent Document 2, the dopant accommodation chamber is arranged at a position that does not interfere with the pulling mechanism; the accommodation chamber is lowered from the upper part in the CZ furnace to a position higher than the upper surface of a quartz crucible; and the dopant in the accommodation chamber is melted at this position by the radiant heat radiated from the melt. Then, the accommodation chamber is further lowered to a position where it contacts with the melt, and the melted dopant is introduced from an opening surface of the accommodation chamber to the melt. Then, the accommodation chamber is further lowered to a position where it contacts with the melt, and the melted dopant is introduced from the opened surface of the accommodation chamber to the melt. The Patent Document 1 describes an invention in which, by introducing the dopant to the melt during the pulling process, a silicon single crystal ingot having different specific resistances, each of which discontinuously changes in a growth axis direction, is pulled up to grow in order to obtain a product that has dopant concentrations in accordance with user's purpose or specifications, etc.
Patent Document 1: Japanese Patent Application Laid-open (Translation of PCT Application) No. 2003-532611
Patent Document 2: Japanese Patent Application Laid-open No. 2005-336020